Space/time characteristics of pressure fluctuations in separation regions

Local wavenumber/frequency characteristics of pressure fluctuations associated with two types of flow separation over the roof of a surface-mounted prism are examined. The first type is the separation formed by a flow normal to one side of the prism. In this separation region, the flow is highly unsteady and reattachment takes place intermittently at varying locations. The second type is the separation formed by a flow at 45° to two sides of the prism. In this separation, two conical vortices form over the prism. Frequency analysis of the surface pressure fluctuations shows broadband spectra at many locations under both types of separation regions. The local wavenumber–frequency spectrum is estimated by using pressure measurements from two taps. In both separation regimes, the measurements show that, at the onset of separation, low frequencies and small wavenumbers dominate the surface pressure fluctuations. Further downstream, where intermittent reattachment or vortex breakdown takes place, the level of energy of the high frequency and large wavenumbers increases. Local wavenumber spectra for the pressure fluctuations are also presented and discussed.